netdev - Re: [RFC net-next v3 2/2] net/mlx5e: Add per queue netdev-genl stats

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Date: Tue, 4 Jun 2024 00:36:16 +0300
From: Tariq Toukan <ttoukan.linux@...il.com>
To: Joe Damato <jdamato@...tly.com>, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, nalramli@...tly.com,
 Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Richard Cochran <richardcochran@...il.com>,
 "open list:MELLANOX MLX5 core VPI driver" <linux-rdma@...r.kernel.org>,
 Tariq Toukan <tariqt@...dia.com>
Subject: Re: [RFC net-next v3 2/2] net/mlx5e: Add per queue netdev-genl stats



On 03/06/2024 22:22, Joe Damato wrote:
> On Mon, Jun 03, 2024 at 02:11:14PM +0300, Tariq Toukan wrote:
>>

...

>>
>> I still don't really like this design, so I gave some more thought on
>> this...
>>
>> I think we should come up with a new mapping array under priv, that maps i
>> (from real_num_tx_queues) to the matching sq_stats struct.
>> This array would be maintained in the channels open/close functions,
>> similarly to priv->txq2sq.
>>
>> Then, we would not calculate the mapping per call, but just get the proper
>> pointer from the array. This eases the handling of htb and ptp queues, which
>> were missed in your txq_ix_to_chtc_ix().
> 
> Maybe I am just getting way off track here, but I noticed this in
> drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c in
> set_pflag_tx_port_ts:
> 
>    if (!err)
>      priv->tx_ptp_opened = true;
> 
> but what if enable is false, meaning the user is disabling ptp via
> ethtool?
> 

This bool field under priv acts as a flag, means: ptp was ever opened.
It's the same idea as max_opened_tc, but with boolean instead of numeric.

> In that case, shouldn't this be:
> 
>    if (!err)
>      priv->tx_ptp_opened = enabled;
> 
> Because it seems like the user could pass 0 to disable ptp, and with
> the current code then trigger mlx5e_close_channels which would call
> mlx5e_ptp_close, but priv->tx_ptp_opened might still be true even
> though ptp has been closed. Just a guess as I really don't know much
> about this code at all, but it seems that the MLX5E_PFLAG_TX_PORT_TS
> will be set in set_pflag_tx_port_ts based on enable, which then
> affects how mlx5e_open_channels behaves.
> 
> Likewise in mlx5e_ptp_close_queues, maybe
> rx_ptp_opened and tx_ptp_opened should be set to false there?
> 
> It seems like the user could get the driver into an inconsistent
> state by enabling then disabling ptp, but maybe I'm just reading
> this all wrong.
> 
> Is that a bug? If so, I can submit:
> 
> 1. ethtool tx_ptp_opened = false
> 2. rx_ptp_opened = tx_ptp_opened = false in mlx5e_ptp_close_queues
> 
> to net as a Fixes ?
> 
> I am asking about this from the perspective of stats, because in the
> qos stuff, the txq2sq_stats mapping is created or removed (set to
> NULL) in mlx5e_activate_qos_sq and mlx5e_deactivate_qos_sq /
> mlx5e_qos_deactivate_queues, respectively.
> 
> This means that priv->txq2sq_stats could be a valid sq_stats or
> invalid for deactivated TCs and qos. It seems like ptp should work
> the same way, but I have no idea.
> 
> If ptp did work the same way, then in base the code would check if
> ptp was disabled and obtain the stats from it, if there are any from
> it being previously enabled.
> 
> That seems like more consistent behavior, but sorry if
> I'm totally off on all of this.
>